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In this Olympics season, I wasn't surprised that the subject of transgender athletes came up in my recent online chat, specifically trans women competing against those "born female," as the writer described. The issue: With new Olympic guidelines in place, do trans women athletes have an unfair advantage?

"I'm LBGTQ-friendly (use the bathroom of your gender identity, marry the person you love, etc.), but the one issue I can't quite resolve in my head is athletics. Transgender females - biologically they would tend to be taller, faster and stronger than those born female, particularly if they are not taking any hormones (though there is a spectrum of these strengths across both genders). What are your thoughts?"

Indeed, there was a time when all this seemed pretty simple. We had men and women, boys and girls - but we now know that gender is anything but simple.

This charged debate is timely because of a landmark rule change instituted by the International Olympic Committee this year. In Rio, transgender men (female-to-male athletes) will be allowed to compete without any restrictions (based on the sexist assumption, I suppose, that trans men could never dominate their sports). Trans women, meanwhile, are no longer required to undergo gender-reassignment surgery to compete in female divisions, and the previously mandated two-year wait after transitioning has been jettisoned.

To compete, a trans woman athlete is required only to declare her gender as "female" and have testosterone levels comparable to or below those of cisgender women. (Cisgender refers to folks whose biological sex matches their gender identity, the opposite of transgender.) These long-awaited changes are a big step forward in creating an equitable playing field - and they bring the IOC in line with the NCAA, which invoked a similar policy for college athletes.

Still, I understand why this rule change is so controversial, especially for female athletes. In my mind, I first imagined a young Bruce Jenner, tall and muscular, competing as Caitlyn Jenner and snaring all the gold medals in the women's events. I imagined wrong, as it turns out, because I was unaware of the medical science behind the IOC decision.

One competitive cisgender female runner, who did not want her name used, explained how "incredibly unfair" this is to her, attributing the rule change to the IOC's "trying to be politically correct." Another cisgender female athlete, former Olympic judo competitor Ronda Rousey, went further (and got graphic) when she complained to the media about her competitor Fallon Fox, a trans woman, claiming: "She can try hormones, chop her pecker off, but it's still the same bone structure a man has. It's an advantage. I don't think it's fair."

But here's why we all had it wrong: The first-ever study of transgender athletes showed that the hormone therapy that facilitates male-to-female transition does more than just suppress testosterone. Published last year in the Journal of Sporting Cultures and Identities, the study showed that as testosterone levels approach female norms, trans women experience a decrease in muscle mass, bone density and other physical characteristics.

"Together these changes lead to a loss of speed, strength and endurance - all key components of athleticism," the study's author, Joanna Harper, wrote in The Washington Post. Harper, who is chief medical physicist at Oregon's Providence Portland Medical Center, a trans athlete and a participant in the IOC meeting that overhauled the trans guidelines, explained to me that "it's not the anatomy that matters, it's the hormones." After a year of hormone therapy, for example, female trans distance runners completely lose their speed advantage over cisgender women.

Okay, so science is science, but are the new rules fair? The IOC, no pushover when it comes to hormones and meds, said it wanted to make sure "that trans athletes are not excluded from the opportunity to participate in sporting competition" and that the overriding objective is "the guarantee of fair competition." But what constitutes fair in sport?

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"Every athlete, whether cisgender or transgender, has advantages and disadvantages," said Cyd Zeigler, author of Fair Play: How LGBT Athletes Are Claiming Their Rightful Place in Sports and a co-founder of Outsports. Chris Mosier, the first out trans man to compete on the men's U.S. national team at the International Triathlon Union Duathlon World Championship in June, expanded on that: "People come in all shapes and sizes," he said. "We don't disqualify Michael Phelps for having super-long arms; that's just a competitive advantage he has in his sport. We don't regulate height in the WNBA or NBA; being tall is just an advantage for a center. For as long as sports have been around, there have been people who have had advantages over others. A universal level playing field does not exist."

Still, the controversy and trans-shaming continue. Although there are well over 40 openly gay and lesbian athletes competing in the Summer Games, neither of the two reported trans athletes has come out publicly. Until anti-trans stigma is fully erased, they are eligible to compete, but, Mosier said, that doesn't mean "everybody is ready to accept us." Now I ask you: Is that fair?